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Research & Publications

In spring 2010 I initiated a field study of Hooded Warblers, Setophaga (formerly Wilsonia) citrina) at Hemlock Hill Field Station located near Cambridge Springs in Crawford County, 16 miles NE of the Allegheny College campus. The primary focus of this study has been the relationship between plumage pattern and foraging performance. In both males and females (pictured below), the outer three tail feathers have extensive white spots that the birds reveal by flicking their tails constantly during foraging. During the May-August nesting season in 2010-2013, I tested the hypothesis that the contrasting white tail spots and tail-flicking behavior increase foraging performance by startling visually oriented winged insect prey that the warblers then pursue and capture in flight. Results strongly supported the hypothesis; birds with experimentally darkened tails (pictured below) had significantly lower prey attack rates than did sham-darkened control birds. In addition, females (but not males) with darkened tails delivered significantly fewer winged prey to their nestlings than did controls.

Since 2014, field work has focused on two related issues. The first is sexual dimorphism in tail pattern; males have slightly more white in the tail than do females, even after controlling for sex differences in body size. I am currently exploring three hypotheses for this sexual dimorphism: (1) sexual selection on the breeding grounds(do females mate preferentially with males with more tail white?), (2) foraging/microhabitat differences on the breeding grounds (do the sex differences in tail pattern reflect sex differences in foraging strategies or microhabitat use during nesting?), and (3) habitat differences on the wintering grounds (do the sex differences in tail pattern reflect evolutionary adaptation to sexual habitat segregation on the Caribbean wintering grounds, whereby males inhabit closed canopy tropical forest and females prefer open scrub habitat?). The second focus of current research is the relationship between tail molt and parental desertion of nestlings and fledglings. Hooded Warblers replace their rectrices (tail feathers) in late summer in preparation for fall migration, and as in other North American warblers,tail molt is practically simultaneous; all 12 rectrices drop within a few days of each other, and a molting bird is without a functional tail for about a week until the replacement feathers are partially grown. Interestingly, about 70% of birds molting their tail before the end of parental care (nearly always males) desert their dependent nestlings or fledglings, leaving the mate (nearly always the female) responsible for all remaining parental care. Because the tail is a critical foraging adaptation for Hooded Warblers, I am testing the intriguing hypothesis that feeding dependent young is especially costly for birds in tail molt, leading to parental desertion. I am also exploring the question of why males molt earlier than females, as this difference in timing of molt appears to at least partially explain why the deserting parent is nearly always male.

Typical tail pattern of Hooded Warblers before (left) and after (right) experimental darkening. The experimental darkening is short-lived, and within a week the tails of experimentally treated birds are indistinguishable from those of unmanipulated birds.

The Myioborus redstarts (also known as whitestarts) comprise 12 species of small insectivorous birds ranging from the southwestern United States to the southern Andes. All 12 species are noted for their white outer tail feathers and their animated foraging displays designed to startle and flush potential insect prey, which can then be pursued and captured in flight. During a spring 2000 sabbatic leave, I initiated a study of the flush-pursuit foraging behavior of the Slate-throated Redstart (Myioborus miniatus) in Monteverde, Costa Rica. I used tail-dyeing experiments to demonstrate that the white outer tail feathers are critical to flush-pursuit foraging success; experimental darkening of tail feathers significantly reduced the probability of flushing potential prey, prey attack rates, and feeding rates at nests. In collaboration with Jorge Pérez-Emán of the Universidad Central in Venezuela and Piotr Jablonski of Seoul National University in Korea, I am currently trying to understand the complex pattern of interspecific and intraspecific geographic variation in the amount of white in the tail and wings of Myioborus redstarts. Although I am no longer conducting field work in Costa Rica, I continue to analyze data collected during my five years of field research there, and examine geographic variation in plumage pattern by examination of museum specimens. My research in Costa Rica was supported by a grant from the Committee for Research and Exploration of the National Geographic Society.

For 15 years my research focused on the behavioral ecology and conservation biology of the Florida Scrub-Jay (Aphelocoma coerulescens), a threatened species that is restricted to the unique oak scrub of peninsular Florida. My research was designed to extend and complement the long-term demographic studies of this species by Glen E. Woolfenden, John W. Fitzpatrick, and their colleagues at Archbold Biological Station in Highlands County, Florida. Florida Scrub Jays are permanently monogamous and permanently territorial. About half of all breeding pairs share their territories with 1-6 nonbreeders that are usually independent offspring of the breeding pair and that usually act as helpers by assisting the resident breeders in rearing the young of subsequent broods. My research pursued four general themes; (1) an experimental analysis of the role of helpers in enhancing reproductive success of recipient breeders, (2) examination of the endocrinological basis of breeding suppression and helping behavior (in collaboration with Steve Schoech of the University of Memphis), (3) the demographic consequences of road mortality on source-sink population dynamics, and (4) the utility of translocation as a technique for restoration of this threatened and declining species.

For my Ph.D. dissertation research at the University of California, Berkeley, I participated in a long-term study of the ecology and social behavior of the Acorn Woodpecker at Hastings Reserve in the upper Carmel Valley, Monterey County, California. The Acorn Woodpecker has perhaps the most complex social system of any North American bird; it lives in permanently territorial family groups of 2-15 birds, generally containing 1-2 breeding females, 1-4 breeding males, and 0-10 nonbreeders that are typically group offspring produced in previous breeding seasons. In groups containing two co-breeding females (usually sisters or mother-daughter combinations), both females lay eggs in a single nest and cooperate to rear the young, a phenomenon called joint nesting. Similarly, in groups with two or more co-breeding males, the males are closely related (brothers or father-son combinations) and compete with one another for access to females during her fertile period prior to egg laying. My dissertation research focused on the mix of cooperation and competition that characterizes this species' complex social system.